1. Field of the Invention
The present invention relates to a fluid flow control device for controlling the amount of fluid flow for the internal combustion engine.
2. Description of the Related Art
Recently, there has been a growing need for increased fuel efficiency (reduced fuel consumption) of an internal combustion engine, and in order to meet this need, various methods have been studied. One of these methods has been proposed to reduce the amount of air which may leak when the throttle valve for opening and closing an air passage for air supply is in a completely closed position, in order to improve fuel efficiency during idling of the internal combustion engine. Japanese laid-open patent publication No. 8-14069 discloses an intake apparatus in which a coating film having an non-stick properties is formed on at least one of an outer peripheral end surface of a throttle valve and a portion of an inner peripheral surface of an air passage which faces the throttle valve.
The coating film used in the known intake apparatus has an non-stick properties against oil drops. However, once an oil drop sticks to the surface of the coating film, the sticking oil drop may form the core of deposit buildup. Therefore, it is necessary to allow for deposit buildup in determining a clearance between the throttle valve and the inner peripheral surface of the air passage. In this case, when the throttle valve is in the completely closed position, air leaks through the clearance between the throttle valve and the inner peripheral surface of the air passage. Therefore, the known technique can provide only a limited improvement in fuel efficiency during idling of the internal combustion engine. Further, prevention of deposit buildup is desired not only in the intake apparatus for an internal combustion engine, but in various other fluid flow control devices provided in a fluid passage through which fluid for the internal combustion engine flow.